Effect of deviation angle between principal stress and diagonal reinforcement direction on seismic performance of RC coupling beams

摘要

In a coupled shear wall system, the reinforced concrete (RC) coupling beams are allowed to form plastic deformations in order to dissipate seismic energy while maintaining the stability of overall structural system. However, the coupling beams are generally shear-dominated members because of their short shear span-depth ratio, which is usually less than 2. Therefore, under high seismic shear demand, the energy dissipation capacity and ductility of these members are sharply reduced compared to RC beams with larger shear span-depth ratio due to severe pinching effect. In order to avoid any undesirable structural behavior, the current standards stipulate the use of diagonal reinforcing bars in RC coupling beams with short span-depth ratio. Previous studies show that the diagonal reinforcement arrangements improve the structural performance of coupling beams, but the behavior of such members under cyclic bending and shear may significantly vary depending on the orientation of diagonal reinforcement. In this study, the effects of deviation angle between principal stress and diagonal reinforcement direction in the failure region, were experimentally investigated considering the potential failure modes of the coupling beams. Six RC coupling beams were tested under reversed cyclic bending and shear during this research. Experimental results show that the ductility ratio and the energy dissipation capacity of RC coupling beams vary, depending on the orientation of the diagonal reinforcement even when the same amount of diagonal reinforcement is provided. The structural performance of RC coupling beams improves as the deviation angle between direction of principal stress and the diagonal reinforcement becomes smaller. Finally, a finite element method (FEM) analysis was carried out for the WA specimens. The FEM analysis results closely agreed with experimental observations that both the ductility ratio and energy dissipation capacity were larger for members with lowest deviation angle.